Every day, thousands of pounds of meteor debris enter Earth’s atmosphere and eventually settle on the surface. Only a small fraction of these particles is large enough to be seen as shooting stars; most burn up high in the atmosphere, leaving behind a haze of tiny particles—meteoric smoke—suspended about 70–100 kilometers above Earth’s surface. The dust is mostly 4.6-billion-year-old leftovers from the messy accretion process of solar system formation, which the planet picks up as it passes through long-decayed comet tails and remnants of asteroid belt smash ups.

Estimates vary greatly as to how much cosmic dust lands on Earth, ranging from 0.4 to 110 tons a day. Those larger numbers stem from measurements made on spacecraft solar panels and accumulation rates of cosmic elements found in polar ice cores, which are largely in agreement with each other. Measurements based on radar observations of meteoric smoke, however, indicate that the amount of cosmic dust making it to the surface is on the lower side of that range.

To narrow that range, Gardner et al. collected Doppler lidar measurements of sodium and iron particles made at the Starfire Optical Range in New Mexico and combined them with model predictions of how these particles—thought to be the remnants of cosmic dust—are transported. From this information the authors estimated the rate of cosmic dust entering Earth’s atmosphere every day. Their estimate landed right in the middle of the existing range, indicating that roughly 60 tons of cosmic dust infiltrate the atmosphere.

These meteoric smoke particles are not just depositing significant amounts energy and mass into the atmosphere, however. They are also influencing processes that scientists are only just beginning to understand. Studies have shown that the cosmic dust can contribute to cloud formation in the upper atmosphere and can fertilize the growth of plankton in Antarctica. The team says that determining the exact amount of cosmic dust hitting the atmosphere will help them understand the role these particles play in an increasing number of other phenomena. (Journal of Geophysical Research: Space Physics, doi:10.1002/2014JA020383, 2014)

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